Let your money work for you. That's the idea behind passive income. There are multiple ways to put your money to work, but some offer greater income than others do.

Closed-end funds (CEFs) stand out as a great alternative for investors to consider. They are mutual funds that can be traded on a stock exchange similar to an exchange-traded fund (ETF). And CEFs often provide exceptionally attractive yields. Here are three high-yield funds that are passive income money machines.

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1. Aberdeen Global Dynamic Dividend Fund

Aberdeen Global Dynamic Dividend Fund (AGD) primarily seeks to provide high dividend income. The fund's secondary investment objective is to generate long-term capital growth. The CEF's net assets totaled $139.7 million as of July 31, 2022.

With these two goals in mind, the fund's top holdings make a lot of sense. Those largest positions include dividend stocks that also have solid growth prospects, including Apple, Microsoft, and AbbVie.

The CEF currently offers an ultra-high dividend yield of close to 7.8%. Its net expense ratio stands at 1.18%. Aberdeen Global Dynamic Dividend Fund trades at a 10.1% discount to its net asset value (NAV). 

2. AllianceBernstein Global High Income Fund

AllianceBernstein Global High Income Fund (AWF -0.39%) is another CEF that primarily attempts to provide high levels of income with a secondary objective of capital appreciation. This fund adjusts its portfolio risk level based on how markets are performing, reducing risk in volatile markets and taking on more risk during favorable markets. 

The CEF invests mainly in corporate debt securities and government bonds. AllianceBernstein fund managers prefer a global multisector approach that provides an attractive risk-return proposition. Currently, more than 72% of the fund's portfolio is invested in U.S. assets.

AllianceBernstein Global High Income's distribution yield is nearly 7.6%. The fund's net expense ratio is 1%. It trades at a 5.3% discount to its NAV. 

3. BlackRock Enhanced Global Dividend Trust

Like the previous two CEFs mentioned, BlackRock Enhanced Global Dividend Trust's (BOE -0.20%) primary investment objective is to provide income, with its secondary objective to provide long-term capital appreciation. Its net assets topped $721 million as of Aug. 22, 2022.

The fund usually invests at least 80% of its net assets in dividend stocks. And at least 40% of its portfolio is typically invested outside of the U.S. Top holdings include Microsoft, Sanofi, Novo Nordisk, and Reckitt Benckiser Group.

BlackRock Enhanced Global Dividend Trust's distribution yield currently stands at over 7.4%. The fund boosts its income by writing covered call and put options, usually on between 30% and 45% of its total assets. Its net expense ratio is 0.90%. The CEF is also available at a 10.5% discount to its NAV.

A couple of things to note 

All three of these closed-end funds truly are passive income money machines. However, there are a couple of important things that investors should know about the funds.

First, don't look for significant capital appreciation from any of these three CEFs. Sure, all of them include capital growth as their secondary investment objectives. But most (if not all) of their total returns will be driven by distributions. 

Second, these funds' share prices can be highly volatile. All three have fallen more year to date than the S&P 500 has.

The volatility for some CEFs can be higher by the use of leverage (borrowing). The good news, though, is that none of these funds use leverage extensively. BlackRock Enhanced Global Dividend Trust doesn't use leverage at all. The effective leverage rates for Aberdeen Global Dynamic Dividend Fund and AllianceBernstein Global High Income Fund are only 4.84% and 0.11%, respectively.