Hi!

I'm repairing an old Canon 600mm F4L lens. I've got the circuit schematic but have a hard time to understand the circuit. The UAout and UBout pulses 0-29V and 0-6V respectively with a phase difference of ~90 degree at ~30kHz. Vb is 29V. I dont understand how Tr5 and Tr7 ever can sink any current since the emitter voltage is 0V at the same time as the signal voltage at the base is 0V?

The reason why I want to understand this is because I dont get the correct drive signal to the USM (sinusoidal waveform). I only get 0-29V pulses, same as the input when I at least should get a real square wave (+-29V) which gets smoothed out by the inductors?

If anybody can explain how this amplifier circuit is designed to work I would be very grateful. Attached is part of the schematic showing the amplfier circuit and some component values as well as pinouts from the IC.

 

Welcome to AAC!

The UAout and UBout pulses 0-29V and 0-6V respectively

I would expect UAout and UBout both to be 0-29V (apart from the phase difference).

I only get 0-29V pulses, same as the input when I at least should get a real square wave (+-29V) which gets smoothed out by the inductors?

The circuit looks to me to be a fairly conventional H-bridge drive to the motor. In one half-cycle when one motor terminal goes to ~ 28V the other terminal goes to 0V, then the situation reverses in the next half cycle, giving a square-wave drive of ~ 56V peak-to-peak across the motor.

 

Welcome to AAC!

I would expect UAout and UBout both to be 0-29V (apart from the phase difference).

The circuit looks to me to be a fairly conventional H-bridge drive to the motor. In one half-cycle when one motor terminal goes to ~ 28V the other terminal goes to 0V, then the situation reverses in the next half cycle, giving a square-wave drive of ~ 56V peak-to-peak across the motor.

Consider that there are two phases, A and B. The only way I can see it work is if Tr5 and Tr7 would have a positive voltage at the emitter when Tr4 and Tr6 is not forward biased. The question is, where would this voltage come from? Maybe it is obvious, but I'm not very skilled with amplifier circuits so if you have an idea how it could work, please explain.

 

UAout and UBout should both have 29 volt pulses. I think eitherTr6 or D2 are defective but it could be the motor as well. If it is the motor then disconnecting UB at the motor should give you the full 29 volt pulse instead of 6 volts.

 

The only way I can see it work is if Tr5 and Tr7 would have a positive voltage at the emitter when Tr4 and Tr6 is not forward biased. The question is, where would this voltage come from?

First half cycle:
UAout is high (29V), so Tr4 is on, Tr5 is off, hence terminal UA is high (about 28V, because of the voltage drop across Tr4). UBout is low (oV), so Tr6 is off, Tr7 is on, hence UB is low.
Second half cycle:
UAout is low, so Tr4 is off, Tr5 is on, hence terminal UA is low. UBout is high, so Tr6 is on, Tr7 is off, hence UB is high.
VB provides the +29V in both half cycles.
If UBout is only 6V then the driver IC or ZD6 could be faulty. If R12 is a low value and Tr7 were short-circuit then that too could pull down UBout.

 

First half cycle:
UAout is high (29V), so Tr4 is on, Tr5 is off, hence terminal UA is high (about 28V, because of the voltage drop across Tr4). UBout is low (oV), so Tr6 is off, Tr7 is on, hence UB is low.

This part is clear although there is an overlap between phase A and B, so B is actually high for part of the time that A is high. (see attached measurement where both phases are measured at the USM phase A and B before the inductor, emitter of TR5 and TR7)

Second half cycle:
UAout is low, so Tr4 is off, Tr5 is on, hence terminal UA is low. UBout is high, so Tr6 is on, Tr7 is off, hence UB is high.
VB provides the +29V in both half cycles.
If UBout is only 6V then the driver IC or ZD6 could be faulty. If R12 is a low value and Tr7 were short-circuit then that too could pull down UBout.

Maybe you misunderstood me, UBout is 0-6V according to the pinout in attached schematics. I think it is strange too, so it could be a typo, but I will measure when I come home from work today. My question is how Tr5 (and Tr7 as well) can be on when UAout (UBout) is low? The voltage at the emitter of Tr5 and Tr7 will also be low?

 

My question is how Tr5 (and Tr7 as well) can be on when UAout (UBout) is low?

Tr5 (Tr7) is a PNP type, so will be on when its base is low, because its emitter voltage is above the base voltage by virtue of the motor having ~28V at its UB (UA) terminal at that time.
Seeing the scope waveforms, it seems the motor is being driven with a so-called 'modified sine-wave', i.e a square-wave with intermittent zero voltage sections across the terminals.

 

Tr5 (Tr7) is a PNP type, so will be on when its base is low, because its emitter voltage is above the base voltage by virtue of the motor having ~28V at its UB (UA) terminal at that time.
Seeing the scope waveforms, it seems the motor is being driven with a so-called 'modified sine-wave', i.e a square-wave with intermittent zero voltage sections across the terminals.
View attachment 177817

Thank you for a good explanation. I resoldered the motor and measured today. Now I got an expected although distorted waveform.

Time to search for bad capacitors.

 

I hope you get the lens working, it's a great lens.

 

Question:

The surface mount tantalum capacitors are marked A6, DS6 etc. I know the uF rating of it in the schematics, but what is the other

 

The Precious post was incomplete.

Question:

The surface mount tantalum capacitors are marked A6, DS6 etc. I know the uF rating of it in the schematics, but what is the other marking? Is "A" and "D" case size and the number voltage?

 

Hi!

I'm repairing an old Canon 600mm F4L lens. I've got the circuit schematic but have a hard time to understand the circuit. The UAout and UBout pulses 0-29V and 0-6V respectively with a phase difference of ~90 degree at ~30kHz. Vb is 29V. I dont understand how Tr5 and Tr7 ever can sink any current since the emitter voltage is 0V at the same time as the signal voltage at the base is 0V?

The reason why I want to understand this is because I dont get the correct drive signal to the USM (sinusoidal waveform). I only get 0-29V pulses, same as the input when I at least should get a real square wave (+-29V) which gets smoothed out by the inductors?

If anybody can explain how this amplifier circuit is designed to work I would be very grateful. Attached is part of the schematic showing the amplfier circuit and some component values as well as pinouts from the IC.

Is it possible to get the documentation on the usm?

 

hi, I'm a student studying ultrasonic motor recently. Due to the problem of funds, I only bought the ultrasonic motor in Canon camera and intend to make a driver circuit myself. I really need the circuit schematic you mentioned in your question and would greatly appreciate it if you could kindly provide it to me.