Search found 23 matches

by trident
Sat Nov 08, 2008 7:14 pm
Forum: General Discussion
Topic: help with op amp circuit
Replies: 16
Views: 3282

Hello I have the project on breadboard now and found I needed to reduce the value of the zener resistor [R6] from 10K to 1.2K to get the zener into the breakdown region. I replaced the LM317 with an LM1117 and do not need the protection diode, but the capacitor values had to be increased. I also dis...
by trident
Sun Aug 24, 2008 3:22 pm
Forum: General Discussion
Topic: help with op amp circuit
Replies: 16
Views: 3282

Hello

Yes that is the correct pin out on the 317.
The 120mm fan I want to use will not start reliably at 5 volts so I will use a 6.0V, 0.5W (1N5233B) zener. I need to look through my spare parts and see what I need to order and then find my trusty Global Specialties breadboard.

Thank You

trident
by trident
Sat Aug 23, 2008 11:40 am
Forum: General Discussion
Topic: help with op amp circuit
Replies: 16
Views: 3282

Hello MrAl
If I may impose, one last question and I shall leave you in peace.
With the Zener solution, Is the wattage of the Zener critical ?

Thank You very much for your time, expertise and patience

trident
by trident
Sat Aug 23, 2008 7:31 am
Forum: General Discussion
Topic: help with op amp circuit
Replies: 16
Views: 3282

Hello again
Thank you for the divider example MrAl
Here is the revised circuit, I put in the variable resistor so the minimum fan voltage can be tuned.
Your resistor values seem a bit low, is not the adjust current on the LM317 100 uA ?

Thank You, trident
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by trident
Sat Aug 23, 2008 5:44 am
Forum: General Discussion
Topic: help with op amp circuit
Replies: 16
Views: 3282

Thank You for your reply MrAl This circuit will be used inside a PC so thermal drift is important, if I may impose, which method will be more temperature stable ? I am using the LM317 for short-circuit protection, the extra 1 volt or so I would gain by using a pass transistor is not critical as I ca...
by trident
Fri Aug 22, 2008 8:11 pm
Forum: General Discussion
Topic: help with op amp circuit
Replies: 16
Views: 3282

help with op amp circuit

working on a circuit to control 3-wire brushless fan with INTEL 4-wire fan PWM signal.
is their a way to set a minimum fan voltage by adding a zener diode or voltage divider ?
comments, suggestions
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by trident
Wed Aug 20, 2008 5:20 pm
Forum: General Discussion
Topic: Replacing the tin can style 741 opamp
Replies: 10
Views: 3073

I have some 741s in the can package. PM me with your address and I can mail one to you, no charge
by trident
Wed Aug 20, 2008 3:36 pm
Forum: General Discussion
Topic: Intel 4-wire pwm fan control
Replies: 0
Views: 1176

Intel 4-wire pwm fan control

need help with low part count circuit to interface 3-wire DC fan to INTEL 4-wire pwm fan output on motherboard. Direct pwm drive will spoil the tachometer output of the 3-wire fan. The pwm control signal is 25kHz, 3.3Vpp, 5mA maximum sink. Want to use high side drive to preserve fan tachometer outpu...