ADAPTIVE ANALOGUE POWER FILTER FOR DC POWER SUPPLIES

Field of the Invention

The present invention relates to filtering the noise on the DC power lines.

Background of the Invention A filter is needed in order to improve the operation of circuits affected from unwanted noises generated in the output of the switching DC-DC power supplies. The generated noise can be absorbed with active and passive circuits.

The simplest example of decreasing noise and oscillations is the capacitor having low ESR value to be connected parallel to the converter output. Using these capacitors causes increase in cost and size as well it causes capacity overflow that will affect the operation of the converters. Another method is LC filter. LC filter structure is successful in performance in low and gradually changing load values. However it may cause problems in loads with high current changes and in frequencies close to the resonance frequency of the filter. Furthermore, the physical growth of inductor and not being able to be found are problems for high current values. A third solution is to connect the linear regulators to the circuit in series. In case this structure is used, efficiency significantly drops and heating problem occurs due to the increase in the current.

Active filter circuit

has high suppression value in small volume,

does not use LC circuits that can cause oscillation and unstable state, does not create fluctuation in output voltage with current change of the load, - has suppression characteristic which be adjusted easily,

enables to conduct heat to the chassis in a planar way, can increase the filter current with its parallelizable structure,

can exhibit automatic filtering characteristic, thus the discharged heat decreases,

can increase the suppression value with serial use.

Passive filter circuit;

the heat which is discharged can be little thereon,

its design and material selection are simple. Active filter solution has the best success in both increasing efficiency and suppressing noise. The reason for this is that it can respond compatible and quickly to both variable load current and variable output voltage. In present active filter applications, linear regulators are essentially used, and the desired filter suppression is provided by adjusting the input-output headroom on the said material. In case the input voltage comes higher than the expected with this application, the heat discharged through the linear regulators increases, efficiency decreases, the heat generated increases; and in case the input voltage comes lower than the expected, the desired filter suppression cannot be provided. The noise which the power supplies have in their outputs by nature

may create unwanted signals on the transmit frequencies in RF circuits, may degrade the receiver sensitivity in RF circuits,

may effect the output signal in operational amplifier circuits,

may cause audible unwanted noise in audio circuits,

- may cause unwanted electromagnetic broadcast and even leakage currents towards input line upon the current form drawn from the load thereon becomes unstable,

may cause wrong measurements in analogue digital converters and sensor circuits.

Summary of the Invention The objective of the present invention is to provide an adaptive active analogue power filter which enables to filter the unwanted noise on the electronic circuits in high levels. Another objective of the present invention is to provide an adaptive active analogue power filter wherein feedback is enabled in order to decrease heat discharge according to load current.

This invention is an adaptive active analogue power filter which finds the positive peak value of voltage level applied on its input and average voltage value level, finds the lowest value of input voltage by using these two information, and suppresses the oscillations at least 25dB in bandwidth of 500Hz-500kHz in highest 250 m Vp-p AC voltage level on power lines which has DC output voltage of 5V-30V by using control circuits adjusting the input-output headroom connected to load charge.

Detailed Description of the Invention

An adaptive active analogue power filter developed to fulfill the objective of the present invention is illustrated in the accompanying figures wherein,

Figure 1 is the schematic view of the blocks which the topic of invention adaptive active analogue power filter comprises.

Figure 2 is the circuit diagram of the Positive Peak Finder which finds the positive peak point of the power line.

Figure 3 is the circuit diagram of the Low-pass filter which enables to find the average voltage value of the DC power line.

Figure 4 is the circuit diagram of the Differential Amplifier which differentiates the output of the low-pass filter from the positive peak.

Figure 5 is the circuit diagram of the Minimum Voltage Finder which finds the lowest level found on the DC power line on the filter input. Figure 6 is the circuit diagram adjusting the input-output voltage headroom.

Figure 7 is the circuit diagram of the Current Detector calculating the current drawn over the load.

Figure 8 is the circuit diagram of Targeted Filter Output Voltage enabling to generate targeted output voltage depending on current drawn over the load.

Figure 9 is the circuit diagram of the MOSFET driver.

Figure 10 is the circuit diagram of the MOSFET generating filtered voltage.

Figure 11 is the circuit diagram of 34V boost converter.

Figure 12 is the wave form of the positive peak of the noise measured with oscilloscope.

Figure 13 is the wave form of the average voltage value of DC power line's in the filter input measured with oscilloscope.

Figure 14 is the wave form of the lowest noise level of the DC power line in the filter input measured with oscilloscope.

Figure 15 is the wave form of the filter output measured with oscilloscope. Figure 16 is the graphical view of the frequency response without load. Figure 17 is the graphical view of the frequency response under 100mA load.

The components shown in the figures are each given reference numbers as follows:

1. Adaptive active analogue power filter

2. Positive Peak Finder

3. Low-pass filter

4. Differential Amplifier

5. Minimum Voltage Finder

6. Window Voltage

7. Targeted Filter Output Voltage 8. Current detector

9. Current Sensitive Filter Selecting Circuit

10. Targeted Filter Output Voltage

11. Active Filter MOSFET

12. MOSFET Driver

13. Filter output

100. DC power line on the filter input

101. Low-pass filter

102. Resistor

103. Capacitor

104. Filtered signal

105. Operational Amplifier

106. Positive peak point of the noise

107. Diode

108. Capacitor

110. Average voltage value

120. Half-value of Peak to Peak voltage intensity

130. Lowest level of input voltage

131. Reference voltage generator

132. Reference voltage level

133. Resistors adjusting headroom

134. Operational amplifier

140. Filter output voltage independent from load current

141. Voltage dividing resistors

142. Current detector IC

143. Positive input of current detector IC

150. Divided voltage equivalent of load current value 160. Filter output voltage sensitive to load current

170. MOSFET driver signal

171. Current sense resistors

172. MOSFET 180. Voltage amplifier

181. 34V voltage output

An adaptive active analogue power filter (1), which enables to filter the unwanted noise on the electronic circuits in high levels, essentially comprises

at least one Positive Peak Finder (2) which is adapted to filter the noise in the filter input and to find the peak level,

at least one low-pass filter (101) which is located in the input of the Positive Peak Finder (2) and adapted to filter the noise in the DC power line (100) in the filter input,

at least one operational amplifier (105) which is located in the Positive Peak Finder (2) and adapted to find the positive peak point (106) of the signal filtered (104) by the low-pass filter (101),

at least one Low-Pass Filter (3) which is adapted to find the voltage value average (110) of the DC power line (100) on the filter input,

at least one Differential Amplifier (4) which is adapted to find the half value (120) of the peak to peak voltage intensity by subtracting the low-pass filter (3) output from the positive peak finder (2),

at least one Minimum Voltage Finder (5) which is adapted to find the minimum voltage level (130) of the DC power line (100) on the filter input, at least one Targeted Filter Output Voltage (7) which is adapted to generate the desired voltage in the filter output,

at least one reference voltage generator (131) which is adapted to filter input- output headroom,

- at least one operational amplifier (134) which is adapted to subtract the resistance divider voltage level adjusting the reference current level (132) generated by the reference voltage generator (131) from the lowest level of the input voltage in the output of the Differential Amplifier (4),

at least one Current Detector (8) which is adapted to measure the current drawn over the load, at least one integrated current detector (142) which is located on the higher part relative to the load as the Current Detector (8) and adapted to convert the voltage decrease of the current drawn over the load into a suitable voltage level,

- at least one Current Sensitive Filter Selecting Circuit (9),

at least one Targeted Filter Output Voltage (10) which is adapted to generate the filter voltage value according to the current drawn over the filter, at least one Active Filter MOSFET (11) which is adapted to filter the noise present in the DC power line (100) in the filter input,

- at least one MOSFET driver (12) which is adapted to drive the N-channel MOSFET (172) used as filtering member,

at least one Boost Converter (180) which is adapted to feed the operational amplifier circuits which are amongst filter members. The main circuit structures used in a preferred embodiment of the inventive adaptive active analogue power filter (1) is shown in Figure 1. The positive peak point (106) of the noise present in DC power line (100) in the filter input is found via the Positive Peak Finder (2) which is one of the main components of the adaptive active analogue power filter (1). The Positive Peak Finder (2) is essentially comprised of a low-pass filter (101) and an operational amplifier (105). In order to start filtering process, first the DC power line (100) in filter input is cleaned from the noises at an undesired high frequency which is over a predetermined value (for example 15MHz) by using the resistor (102) and the capacitor (103) of the low pass filter (101). The positive peak point (106) of the noise present in the filtered signal (104) in the output of the low pass filter (101) is found by using an operational amplifier (105). A signal in the output of the operational amplifier (105) charges the capacitor (108) unilaterally via diode (107). In cases wherein the input voltage level is low, the diode (107) prevents the capacitor (108) to be discharged and enables the positive peak level of the input signal to be found. The circuit structure of the Positive Peak Finder (2) is given in Figure 2, and its test result is shown in Figure 12. The average voltage value (110) of the DC power line (100) in the filter input is found with the circuit structure given in Figure 3 by using a Low-Pass Filter (3). Test result is shown in Figure 13.

Then by means of the Differential Amplifier (4), the half value (120) of the highest peak to peak voltage intensity of the noise present in the DC power line (100) in the filter input is found by subtracting the average voltage value (110) from the positive peak point (106) value of the input voltage present in the DC power line (100) in the filter input. The circuit structure of the Differential Amplifier (4) is shown in Figure 4.

Then, by means of the Minimum Voltage Finder (5), the lowest level of voltage (130) present in the DC power line (100) in the filter input is found by subtracting the half value (120) of the highest peak to peak voltage intensity of the noise in the DC power line (100) in filter input from the average voltage value (110) of the DC power line (100) in the filter input. The circuit structure of the Minimum Voltage Finder (5) is shown in Figure 5, and its test result is given in Figure 14. A reference voltage level (132) is acquired at a desired level (preferably 1.24V) by means of the reference voltage generator (131) adjusting the input-output voltage headroom through the DC power line (100) in the filter input. This reference voltage level (132) is lowered to a desired voltage level (preferably 500mV) by means of the two resistors (133) adjusting input-output headroom. This new Window Voltage (6) level which is acquired is subtracted from the lowest voltage level (130) of the voltage in the DC power line (100) in the filter input via an operational amplifier (134). After this process, the filter output voltage independent from load current (140) is calculated. In case suppression is wanted to be performed with a voltage different than 500mV level, the values of the two resistors (133) adjusting input-output voltage headrooms should be changed. Targeted Filter Output Voltage (7) enabling to generate filter output voltage (140) independent from load current is given in Figure 6 and its test result is shown in Figure 15.

Upon the current drawn over the load increases, the heat discharged from the filters increases. Furthermore, upon the current which is drawn increases, there is a decrease in noise level of DC/DC converters. Therefore the input-output voltage headroom is adjusted with the current drawn by the load by using these two features, that is, input-output headroom is decreased as the current increases. Current Detector (8) calculates the current drawn over the load. The current drawn by the load is passed through the current detecting resistors (171), and the decrease in voltage on these resistors is converted into suitable voltage level by means of the integrated current detector (142). The effect of the detected current level on the input-output headroom is adjusted by means of the voltage dividing resistors (141), and thus the divided voltage equivalent (150) of the load current value of the Current Detector (8). The circuit structure of the Current Detector (8) enabling to calculate the current drawn over the load is shown in Figure 7.

The effect of current drawn from the load is added to the Targeted Filter Output Voltage (7) independent from the load current in order to generate the Targeted Filter Output Voltage (10) dependent on the load current drawn over the load. The divided voltage equivalent (150) of the load current value of the Current Detector (8) adjusts input-output voltage headroom, in other words is added to the filter output voltage (140) independent from the load current drawn from the load, and thus the filter output voltage (160) level sensitive to load current drawn over the load is acquired. Filter output voltage sensitive to load current (160) will be acquired in filter output (13).

The driving of N-channel MOSFET (172) is shown in Figure 9 wherein it is performed by comparing the load current sensitive filter output voltage (160) or filter output voltage independent from load current (140) with the filter output (13). The driving of MOSFET (172) according to comparison is performed via the MOSFET driver signal (170) shown in Figure 9.

The circuit diagram of N-channel MOSFET (172) and current detection resistors (171) are given in Figure 10.

The circuit diagram of the boost converter (180), which boosts the voltage of the DC power line (100) in the filter input to a desired voltage in order to enable to operate the operational amplifiers that are amongst filter members, is shown in Figure 11. In one embodiment of the invention, by means of the 34V voltage output (181), the voltage of the DC power line (100) in the filter input is raised to 34V in order to operate the operational amplifiers.

The performance results of the Adaptive active analogue power filter (1) under load and without load measured with Frequency Response Analyzer device are respectively given in Figure 16 and Figure 17.