Pwm-servo-amplifier

Description: A significant feature of the PWM servo amplifier is the removal of a pulse transformer. A 150 kHz pulse-width modulated signal is applied to U3, with its complementary outputs directed to identical circuits to drive the load. When point A increases, Q2 is activated, and point B is at ground potential. The Vee for U1 is sustained through D1, while Q1 is kept off by D2. When point A decreases, Q2 turns off, and point C is pulled low by C2, which activates Q1. The time constant for R1, R3, and C2 is sufficient to keep Q1 on just long enough to allow the voltage at point B to begin rising. As point B increases, it charges C2 by forward-biasing D3, keeping point C low relative to U1 and maintaining Q1 in an on state. With point B at 40 V, D2 is off, and point C is held low by R1 and R2, while Vee for U1 is sustained by the charge on C1. When point A increases again, Q2 turns on once more, causing C2 to push point C high and turning Q1 off long enough for the voltage at point B to start decreasing. C2 is now discharged by reverse-biased D3, which maintains point C high relative to U1 and keeps Q1 off. Once point B drops to ground potential, D1 turns on again, recharging C1 and sustaining Vee for U1. D2 also turns on, keeping Q1 off.

The PWM servo amplifier circuit operates by utilizing a pulse-width modulation technique to control the output signal without the need for a pulse transformer. The core component, U3, generates a 150 kHz PWM signal that is split into complementary outputs, allowing for efficient driving of the load. The circuit features multiple key components: transistors Q1 and Q2, capacitors C1 and C2, diodes D1, D2, and D3, and resistors R1 and R3.

In the operational sequence, when point A experiences a rising voltage, Q2 is turned on, resulting in point B being held at ground potential. This condition allows D1 to maintain the Vee supply for U1, while D2 ensures that Q1 remains off. As the voltage at point A decreases, Q2 turns off, and capacitor C2 pulls point C low, activating Q1. The combination of resistors R1 and R3, along with capacitor C2, establishes a time constant that keeps Q1 conducting long enough for point B to begin its upward transition.

As point B rises, it forward-biases diode D3, allowing C2 to charge while keeping point C low in relation to U1, thus maintaining Q1 in the on state. When point B reaches 40 V, diode D2 is off, and point C remains low due to the action of resistors R1 and R2, while capacitor C1 continues to supply Vee to U1. A subsequent increase in point A turns Q2 on again, which causes C2 to push point C high, turning Q1 off for a brief period, allowing point B to start falling.

During this phase, C2 discharges through D3, which is reverse-biased, ensuring that point C remains high relative to U1 and Q1 stays off. As point B drops to ground potential, D1 reactivates, recharging C1 and maintaining the Vee supply for U1, while D2 turns on to keep Q1 off. This cycle of operation enables the PWM servo amplifier to effectively manage the load with high efficiency and reliability, eliminating the need for a pulse transformer and enhancing the overall performance of the circuit.A major feature of the PWM servo amplifier is elimination of a pulse transformer. A 150 kHz pulsewidth modulated signal is applied to U3, with its complementary outputs applied to identical circuits to drive the load. When point A increases, Q2 is on and point B is at ground potential. The Vee for Ul is maintained through Dl, and Ql is held off by D2. When point A decreases, Q2 turns off, point Cis pulled low by C2, which turns Ql on. The time constant for Rl, R3, and C2 can hold Ql on just long enough to allow the voltage at point B to start rising.

As point B rises, it charges C2 by forward biasing D3, maintaining point C low with respect to Ul, and keeping Ql turned on. With point B at 40 V, D2 is off and point C is held low by Rl and R2, and Vee for Ul is maintained by the charge on Cl.

When point A increases again, Q2 again turns on, C2 pushes point C high, and turns Ql off long enough to allow the voltage at point B to start falling. C2 is now discharged by reverse-biased D3, which keeps point C high with respect to Ul, and keeps Ql off.

Once point Breaches ground potential, Dl again turns on, recharging Cl, and maintaining Vee to Ul. D2 also turns on and keeps Ql off.