# Transformer output

#### PaPiャSly

Joined Dec 25, 2022
33
Hi, so im trying to use this transformer as powersupply and it already has a rectifier and capacitor to filter the output, my concerns are the following :
-Votlage output from the rectifier is 20v but it charges the capacitor upto 27v
-also scared to use it on my amplifier cuase the current isn't regulated

Im just a newbie so I'm trying to gather more information for my project

#### Alec_t

Joined Sep 17, 2013
13,315
Welcome to AAC.
Voltage output from the rectifier is 20v but it charges the capacitor up to 27v
Are you sure the 20V is from the rectifier and not the transformer? Something could be wrong if 20V on the rectifier gives 27V on the capacitor.
If the transformer has a 20V rating, this is RMS (root mean square), so the peak voltage for a sine wave will be 20 x the square root of 2, = 20 x 1.414 = 28.3V. If the rectifier is a bridge, there will be a voltage drop across two diodes, so the capacitor will charge to 28.3V - 2 x 0.65V = 27V.
also scared to use it on my amplifier cuase the current isn't regulated
Is your amplifier rated to handle a 27V supply? If so, it will draw whatever current it needs.

#### MrAl

Joined Jun 17, 2014
9,751
Regular transformers with rectifiers and capacitors will charge the output up to 1.4 times the nominal AC value in Volts RMS. So if your AC rms voltage is 10 volts it will charge up to 14 volts DC and if AC rms is 20 volts then it will charge up to 28 volts DC, and that is before you apply a load.

To get 20v output constant you need a voltage regulator on the output.

#### dl324

Joined Mar 30, 2015
15,510
Welcome to AAC!
-Votlage output from the rectifier is 20v but it charges the capacitor upto 27v
The peak output voltage at the filter cap will be 20V * 1.414 minus the voltage drop for whatever rectifier you're using; 1 diode drop for half wave, 2 for a bridge rectifier. The output voltage will be higher if the transformer isn't loaded.
-also scared to use it on my amplifier cuase the current isn't regulated
The amplifier will only take what it needs after you regulate the voltage to what it needs. What is the amp's current requirement and what is the transformer secondary rated for?

#### crutschow

Joined Mar 14, 2008
31,477
scared to use it on my amplifier cuase the current isn't regulated
It should be okay if the amp's rated voltage is above 27V.

Depending upon the required maximum current, you could use a regulator such as the common LM317, to give a steady DC out.

#### PaPiャSly

Joined Dec 25, 2022
33
Welcome to AAC.

Are you sure the 20V is from the rectifier and not the transformer? Something could be wrong if 20V on the rectifier gives 27V on the capacitor.
If the transformer has a 20V rating, this is RMS (root mean square), so the peak voltage for a sine wave will be 20 x the square root of 2, = 20 x 1.414 = 28.3V. If the rectifier is a bridge, there will be a voltage drop across two diodes, so the capacitor will charge to 28.3V - 2 x 0.65V = 27V.

Is your amplifier rated to handle a 27V supply? If so, it will draw whatever current it needs.
It's only py rated to handle 24v 5a so im also trying to find a way to regulate the voltage

#### PaPiャSly

Joined Dec 25, 2022
33
Hi, so im trying to use this transformer as powersupply and it already has a rectifier and capacitor to filter the output, my concerns are the following :
-Votlage output from the rectifier is 20v but it charges the capacitor upto 27v
-also scared to use it on my amplifier cuase the current isn't regulated

Im just a newbie so I'm trying to gather more information for my project

#### Attachments

• 2.8 MB Views: 10
• 2.8 MB Views: 10
• 3.2 MB Views: 10
• 1.2 MB Views: 10
• 2.8 MB Views: 10

#### MrChips

Joined Oct 2, 2009
28,094
Feed the output of the transformer into four 1N4001 diodes in series or use an LM7824 voltage regulator.

#### PaPiャSly

Joined Dec 25, 2022
33
Welcome to AAC.

Are you sure the 20V is from the rectifier and not the transformer? Something could be wrong if 20V on the rectifier gives 27V on the capacitor.
If the transformer has a 20V rating, this is RMS (root mean square), so the peak voltage for a sine wave will be 20 x the square root of 2, = 20 x 1.414 = 28.3V. If the rectifier is a bridge, there will be a voltage drop across two diodes, so the capacitor will charge to 28.3V - 2 x 0.65V = 27V.

Is your amplifier rated to handle a 27V supply? If so, it will draw whatever current it needs.
It is only rated for 12-24v 5a but i wanna regulate the transformer output voltage to 20v

#### PaPiャSly

Joined Dec 25, 2022
33
It should be okay if the amp's rated voltage is above 27V.

Depending upon the required maximum current, you could use a regulator such as the common LM317, to give a steady DC out.
Might try this one. Thanks

#### PaPiャSly

Joined Dec 25, 2022
33
Welcome to AAC!
The peak output voltage at the filter cap will be 20V * 1.414 minus the voltage drop for whatever rectifier you're using; 1 diode drop for half wave, 2 for a bridge rectifier. The output voltage will be higher if the transformer isn't loaded.
The amplifier will only take what it needs after you regulate the voltage to what it needs. What is the amp's current requirement and what is the transformer secondary rated for?
It is only rated for 12-24v 5a but i wanna regulate the transformer output voltage to 20v replied on my thread with some pics for the transformer specs

#### WBahn

Joined Mar 31, 2012
28,138
Is the transformer rated to deliver the 5 A that your amplifier might need?

If you want to regulate it with a 78xx regulator IC, then you are going to need to include circuitry to provide current bypassing since those regulators don't like to put out more than 1 A of current (if properly heat-sinked).

#### PaPiャSly

Joined Dec 25, 2022
33
Is the transformer rated to deliver the 5 A that your amplifier might need?

If you want to regulate it with a 78xx regulator IC, then you are going to need to include circuitry to provide current bypassing since those regulators don't like to put out more than 1 A of current (if properly heat-sinked).
I don't really have way to find what mu transformer current rating is

#### Attachments

• 3.2 MB Views: 12

#### Alec_t

Joined Sep 17, 2013
13,315
I don't really have way to find what mu transformer current rating is
What are the transformer core dimensions? If the marking CZ66X36 indicates dimensions of 66mm x 36mm then the transformer is unlikely to be rated above ~1A output current.

#### MrAl

Joined Jun 17, 2014
9,751
It is only rated for 12-24v 5a but i wanna regulate the transformer output voltage to 20v replied on my thread with some pics for the transformer specs
Do you need 20v at 5 amps? That is significant power you may have to use a switching regulator. A linear regulator may eat up too much power and get hot.
You also need significant capacitor filtering to keep the unregulated voltage dips above about 22 volts.